Abuja , Nigeria -LRB- CNN -RRB- -- Boko Haram 's elusive leader claimed responsibility for a bombing in Nigeria 's capital of Abuja that left dozens dead , but said nothing about the group 's reported mass abduction of schoolgirls that occurred the same day as the explosion .

A man claiming to be Abubakar Shekau made the comments in a video posted online on Saturday , saying the group attacked a bus station in retaliation for the what he described as the government 's collusion with the United States in the killing of Muslims .

`` This is a prelude , '' said the man , who wore camouflage and held an AK-47 assault rifle , in the video .

In a warning to Nigerian President Goodluck Jonathan , the man said : `` Let me be blunt : I am in your city , near you . Find me . ''

Mass abduction

The video surfaced the same day that an education official said a Nigerian schoolgirl , who was among the 129 kidnapped Monday by suspected Boko Haram militants , had returned home .

Even so , 84 of the girl 's classmates remain unaccounted for .

A total of 45 girls are now free , according to a statement from Borno State Education Commissioner Musa Inuwa Kulo .

This still unsettled situation began Monday night , when militants engaged in a battle with guards at the Government Girls Secondary School in the northeastern Nigerian town of Chibok began herding the girls onto buses and trucks and drove off , authorities said .

But some of the schoolgirls managed subsequently to escape , including 14 on Friday and others on previous days , according to Kulo .

This is a far cry from the Defense Ministry 's previous report that all but eight of the girls had found freedom , a claim that Nigeria 's military retracted Thursday .

This retraction spurred fervent criticism of the government , with Lawan Zanna -- the father of one of the students -- blasting it as having resorted to `` blatant propaganda '' by making a `` blatant lie . ''

What is Boko Haram ?

While the mass abduction is extraordinary , violence in the region has been on the rise .

That violence was on display Monday when a bomb exploded at the bus station in Abuja during rush hour , killing at least 75 people and wounding more than 100 .

But nowhere has it been more prevalent that in northeastern Nigeria 's Borno , Yobe and Adamawa provinces , which have been under a state of emergency since mid-May due to persistent bloodshed there the government blames on Boko Haram .

The Islamist militant group -- who name means `` Western education is sin '' in the local Hausa language -- has bombed schools , churches and mosques ; kidnapped women and children ; and assassinated politicians and religious leaders alike .

Boko Haram says its aim is to impose a stricter enforcement of Sharia law across Africa 's most populous nation , which is split between a majority Muslim north and a mostly Christian south .

The advocacy group Human Rights Watch claims more than 3,000 people have been killed in Boko Haram-related violence in the past five years .

Who is Shekau ?

Under Shekau , who took control of the group in 2009 , violence carried out by the group has flourished , according to authorities .

Questions have swirled about Shekau , including whether he 's dead or alive . In recent years , the Nigerian military has touted his death , only to retract its claim after he appeared alive and vibrant in propaganda videos .

He uses the alias Darul Tawheed , and analysts describe him as a ruthless loner and master of disguise .

The United States has put a $ 7 million bounty on Shekau 's head . It also designated Boko Haram as a foreign terrorist network last year .

The group is diffuse , and Skekau does not speak directly with members , opting to communicate through a few select confidants . This may be why Shekau made no mention of the kidnapping of the schoolgirls .

CNN 's Faith Karimi and journalist Aminu Abubakar in Kano contributed to this report .

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NEW : In a video , Boko Haram claims responsibility for a bombing at a bus station

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NEW : But the leader of the group says nothing about its kidnapping of 129 schoolgirls

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Government : 45 school girls are free , the fate of the rest is unknown

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The abduction is being blamed on the Islamist militant group Boko Haram